I'll ignore all the fundamental reasons (discussed on this and other threads) and give you a practical one that won't require you to understand constitutional law or political theories on freedom. Do you remember the riots in Los Angeles back in the early 1990s? Do you remember the Korean shop-keepers, who were able to protect their property and their lives (and the lives of their families and neighbors) against the looters with semi-auto rifles?
Those rifles are the ones being classified as "assault weapons" under this law. The law isn't banning machine guns (those were regulated in the early 1930s, and the only legal one ever used in a crime was owned by a police officer who would be immune to the restrictive regulations in any case, since such laws nearly alway exempt government agencies).
In addition, this law bans magazine capacities above 10 rounds. The result is that the Korean shop-keeper in the same situation wouldn't have the luxury of being able to fire "warning shots" like they did in that situation; they would have no choice but to shoot to kill or be murdered by the mob attacking them (and if the mob wasn't deterred, possibly both).
I realize that you probably don't have the time or the desire to do the research (but if you do, you can verify this information easily), but you should realize that according to the statistics these guns simply aren't used in crimes more than a tiny fraction of a percent (.26 of 1% according to the last FBI numbers I saw). In addition, they have the illusion of being dangerous to those that don't know any better, but the fact is that the intermediate cartridge they shoot is far less powerful (and less deadly) than the typical hunting rifle round.
In other words, just about all the arguments against them are based on lies; and lies are a bad foundation for public policy, even ignoring the Constitutional issues.